This invention relates to compliant thrust bearings, and more particularly to a resilient support system for compliant bearings formed of a bundle of nested Belleville springs.
The compliant hydrodynamic fluid thrust bearing has shown itself to be nearly ideal for many applications in which other forms of bearings are completely unsuitable. For example, certain ultra-high-speed and high-temperature applications require fluid film bearings which can accommodate varying load conditions and dimensional changes due to temperature and speed. The compliant hydrodynamic fluid film thrust bearing fills this need by enabling the bearing surface to conform to the shape and deflection patterns of the thrust runner, and therefore, is able to operate satisfactorily in conditions under which other bearings, even other fluid film bearings, would fail.
Although this bearing has performed well in past applications, there are anticipated applications in the future which will make even greater demands on its performance characteristics. In particular, it is anticipated that the speed and capacity demands on the bearing will increase significantly in anticipated future uses, and the capacity of the bearing as it is presently designed will be exceeded by these future applications.
The resilient support for the bearing sheet in bearings of this nature has two basic functions. It must enable the bearing sheet to assume the correct hydrodynamic shape with respect to the thrust runner so that supporting hydrodynamic fluid films are generated by the relative movement of the thrust runner and the bearing sheet. In addition, the bearing sheet must be supported in a manner to enable it to conform to the thrust runner despite load fluctuations exerted by rotor imbalance, eccentric loading of the rotor and thermal, centrifugal and other dimensional variations which occur in operation. These deflections of the bearing sheet, necessary for optimum performance of a bearing, are not necessarily produced by a uniform spring constant. For example, the spring stiffness which enables the bearing sheet to assume the correct hydrodynamic shape with respect to the thrust runner may be too compliant for optimum support of the thrust runner during normal operation, which in turn may be too stiff to give the desired self-alignment capability under load fluctuations on the rotor. Thus, it is necessary that a designer of bearings of this nature know exactly what response he wants the resilient support element for the bearing sheet to have under what load conditions, and then design the spring characteristic to produce the desired response. The prior art analysis of the desired spring characteristics has not fully appreciated the significance of the dual function of the resilient support of the bearing sheet and, more importantly, has failed to develop a spring system which would satisfy these requirements.